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Imam Abdul Karem, left, leading a prayer at the King Fahad Mosque in Culver City. Benjamin Brayfield/KPCC

It's difficult to quantify how many Muslims live in Southern California. But experts say the region's Muslim community spans every county in the region and encompasses numerous ethnic and national backgrounds.

"The Muslim community is the most diverse in terms of their ethnic backgrounds in the United States," says Shakeel Syed, Executive Director of the Islamic Shura Council of Southern California. "So they come from all continents, all places."

A 2010 survey of religious institutions, including mosques, offers some of the most specific information available about the number of Muslims living in Southern California. The U.S. Religion Census, conducted by the Association of Statisticians of American Religious Bodies, estimated there are 120,868 Muslims living in Los Angeles, Orange, Riverside, San Bernardino and Ventura Counties. While California is the nation's most populous state, it has fewer Muslims than Texas, New York or Illinois.

Those numbers are probably low though, cautions Brie Jeanette Loskota of USC's Center for Religion and Civic Culture. That's likely due to the fact that the survey relies on Mosque attendance, so may miss large parts of the group, including many women. Yet it's still among the most specific available information on Muslims in the region.

The Los Angeles chapter of the Council on American-Islamic relations estimates there are around 500,000 Muslims in the region. The Garden Grove-based Shura Council offers a similar figure for the area spanning Santa Barbara to San Diego County.

Muslims in the region have come under increased scrutiny following last week's shooting in San Bernardino, which killed 14 people. The shooters were a Muslim couple.

Data on religious communities is difficult to come by for any group. That's because, though the U.S. Census asks about sensitive topics from race to income, it doesn't track the religious affiliations of Americans. It hasn't for decades, and since the 1970s the Census has been barred by law from even asking about religion.

State government doesn't track religious groups either.

The demographic picture is unclear nationally for Muslims too, where estimates of the population range from about 2.75 million to as many as 7 million.

That lack of data makes it even harder to quantify the makeup of Southern California's Muslim community. Still, some indications are available in a 2011 survey of mosques in Southern California, done by the Shura Council with a University of Kentucky researcher.

That study found that the makeup of Southern California mosques is significantly more South Asian and Iranian than it is nationally, and somewhat less African-American.

Above: an excerpt from the 2011 study A Comprehensive Survey of Southern California Mosques

Syed, of the Islamic Shura Council of Southern California, said that it's difficult to make any generalization about the Muslim-American population as a whole.

"Is there diversity in the perspectives, in the things they do and don't do? Absolutely, yes."